Control system for a furfural refining unit receiving heavy sour charge oil

ABSTRACT

A furfural refining unit treats heavy sour charge oil with a furfural solvent in a refining tower to yield raffinate and extract mix. The furfural is recovered from the raffinate and from the extract mix and returned to the refining tower. A system controlling the refining unit includes a gravity analyzer, a flash point temperature analyzer, a sulfur analyzer and viscosity analyzers; all analyzing the heavy sour charge oil and providing corresponding signals, sensors sense the flow rates of the charge oil and the furfural flowing into the refining tower and the temperature of the extract mix and provide corresponding signals. One of the flow rates of the heavy sour charge oil and the furfural flow rates is controlled in accordance with the signals from all the analyzers and all the sensors, while the other flow rate of the heavy sour charge oil and the furfural flow rates is constant.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation as to all subject matter common toU.S. application Ser. No. 851,991 filed Nov. 16, 1977, and now abandonedby Avilino Sequeira, Jr., John D. Begnaud and Frank L. Barger, andassigned to Texaco Inc., assignee of the present invention, and acontinuation-in-part for additional subject matter.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to control systems and methods in generaland, more particularly, to control systems and methods for oil refiningunits.

SUMMARY OF THE INVENTION

A furfural refining unit treats heavy sour charge oil with a furfuralsolvent in a refining tower to yield raffinate and extract mix. Thefurfural is recovered from the raffinate and from the extract mix andreturned to the refining tower. A system controlling the refining unitincludes a gravity analyzer, a flash point temperature analyzer, asulfur analyzer and viscosity analyzer. The analyzers analyze the heavysour charge oil and provide corresponding signals. Sensors sense theflow rates of the charge oil and the furfural flowing into the refiningtower and the temperature of the extract mix and provide correspondingsignals. The flow rate of the heavy sour charge oil or the furfural iscontrolled in accordance with the signals provided by all the sensorsand the analyzers while the other flow rate of the heavy sour charge oiland the furfural flow rates is constant.

The objects and advantages of the invention will appear more fullyhereinafter from a consideration of the detailed description whichfollows, taken together with the accompanying drawings wherein oneembodiment of the invention is illustrated by way of example. It is tobe expressly understood, however, that the drawings are for illustrationpurposes only and are not to be construed as defining the limits of theinvention.

DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a furfural refining unit in partial schematic form and acontrol system, constructed in accordance with the present invention, insimple block diagram form.

FIG. 2 is a detailed block diagram of the control means shown in FIG. 1.

FIGS. 3 through 14 are detailed block diagrams of the H computer, the Ksignal means, the H signal means, the KV computer, the VI signal means,the SUS computer, the SUS₂₁₀ computer, the W computer, theVI_(DWC).sbsb.O computer, the VI_(DWC).sbsb.P computer, the A computerand the J computer, respectively, shown in FIG. 2.

DESCRIPTION OF THE INVENTION

An extractor 1 in a solvent refining unit is receiving heavy sour chargeoil by way of a line 4 and furfural by way of a line 7 and providingraffinate to recovery by way of a line 10, and an extract mix torecovery by way of a line 14.

Heavy sour charge oil is a charge oil having a sulfur content greaterthan a predetermined sulfur content and having a kinematic viscosity,corrected to a predetermined temperature, greater than a predeterminedkinematic viscosity. Preferably, the predetermined sulfur content is1.0%, the predetermined temperature is 210° F., and the predeterminedkinematic viscosity is 15.0, respectively. The temperature in extractor1 is controlled by cooling water passing through a line 16. A gravityanalyzer 20, flash point analyzer 22 and viscosity analyzers 23 and 24and a sulfur analyzer 28 sample the charge oil in line 4 and providesignals API, FL, KV₂₁₀, KV₁₅₀ and S, respectively, co-responding to theAPI gravity, the flash point, the kinematic viscosities at 210° and 150°F., the refractive index and sulfur content, respectively.

A flow transmitter 30 in line 4 provides a signal CHG corresponding tothe flow rate of the charge oil in line 4. Another flow transmitter 33in line 7 provides a signal SOLV corresponding the furfural flow rate. Atemperature sensor 38, sensing the temperature of the extract mixleaving extractor 1, provides a signal T corresponding to the sensedtemperature. All signals hereinbefore mentioned are provided to controlmeans 40.

Control means 40 provides signal C to a flow recorder controller 43.Recorder controller 43 receives signals CHG and C and provides a signalto a valve 48 to control the flow rate of the charge oil in line 4 inaccordance with signals CHG and C so that the charge oil assumes adesired flow rate. Signal T is also provided to temperature controller50. Temperature controller 50 provides a signal to a valve 51 to controlthe amount of cooling water entering extractor 1 and hence thetemperature of the extract-mix in accordance with its set point positionand signal T.

The following equations are used in practicing the present invention forheavy sour charge oil:

    H.sub.210 =lnln(KV.sub.210 +C.sub.1)                       1.

where H₂₁₀ is a viscosity H value for 210° F., KV₂₁₀ is the kinematicviscosity of the charge oil at 210° F. and C₁ is a constant having apreferred value of 0.6.

    H.sub.150 =lnln(KV.sub.150 +C.sub.1)                       2.

where H₁₅₀ is a viscosity H value for 150° F., and KV₁₅₀ is thekinematic viscosity of the charge oil at 150°0 F.

    k.sub.150 =[c.sub.2 -ln(T.sub.150 +C.sub.2 ]C.sub.4        3.

where K₁₅₀ is a constant needed for estimation of the kinematicviscosity at 100° F., T₁₅₀ is 150, and C₂ through C₄ are constantshaving preferred values of 6.5073, 460 and 0.17937, respectively.

    H.sub.100 =H.sub.210 +(H.sub.150 -H.sub.210)/K.sub.150     4.

where H₁₀₀ is a viscosity H value for 100° F.

    kv.sub.100 =exp[exp(H.sub.100)]-C.sub.1                    5.

where KV₁₀₀ is the kinematic viscosity of the charge oil at 100° F.

    sus=c.sub.5 (kv.sub.210)+[c.sub.6 +c.sub.7 (kv.sub.210)]/[c.sub.8 +c.sub.9 (kv.sub.210)+c.sub.10 (kv.sub.210).sup.2 +c.sub.11 (kv.sub.210).sup.3 ](c.sub.12)                                               6.

where SUS is the viscosity in Saybolt Universal Seconds and C₅ throughC₁₂ are constants having preferred values of 4.6324, 1.0, 0.03264,3930.2, 262.7, 23.97, 1.646 and 10⁻⁵, respectively.

    SUS.sub.210 =[C.sub.13 +C.sub.14 (C.sub.15 -C.sub.16)]SUS  7.

where SUS₂₁₀ is the viscosity in Saybolt Universal Seconds at 210° F.and C₁₃ through C₁₆ are constants having preferred values of 1.0,0.000061, 210 and 100, respectively.

    W=C.sub.44 -C.sub.44 API+C.sub.45 /KV.sub.210 -C.sub.46 S+C.sub.47 (API).sup.2 -C.sub.48 API/KV.sub.210 +C.sub.49 (A)(API),  8.

where W is the percent wax in the charge oil, and C₄₃ through C₄₉ areconstants having preferred values of 51.17 4.3135, 182.83, 5.2388,0.101, 6.6106 and 0.19609, respectively.

    VI.sub.DWC.sbsb.O =-C.sub.67 +C.sub.68 (KV.sub.210).sup.2 +C.sub.69 (VI)-C.sub.70 (API)(VI)+C.sub.71 (API).sup.2 +C.sub.72 (FL)(VI)-C.sub.73 (W)(KV.sub.210),                                          9.

where C₆₇ through C₇₃ are constants having preferred values of 168.538,0.0468, 3.63863, 0.17523, 0.41542, 0.00106 and 0.21918, respectively.

    VI.sub.DWC.sbsb.P =VI.sub.DWC.sbsb.O +(Pour)[C.sub.21 -C.sub.22 lnSUS.sub.210 +C.sub.23 (lnSUS.sub.210).sup.2 ]           10.

where VI_(DWC).sbsb.P and Pour are the viscosity index of the dewaxedcharge at a predetermined temperature and the Pour Point of the dewaxedproduct, respectively, and C₂₁ through C₂₃ are constants havingpreferred values of 2.856, 1.18 and 0.126, respectively.

    ΔVI=VI.sub.RO -VI.sub.DWC.sbsb.O =VI.sub.RP -VI.sub.DWC.sbsb.P 11.

where VI_(RO) and VI_(RP) are the VI of the refined oil at 0° F., andthe predetermined temperature, respectively.

    A=C.sub.74 -C.sub.75 (KV.sub.210).sup.2 +C.sub.76 (S)+C.sub.77 (FL).sup.2 -C.sub.78 (FL)(API)-C.sub.79 (KV.sub.210)(S),             12.

where C₇₄ through C₇₉ are constants having preferred values of 503.518,0.04423, 54.58305, 0.00055, 0.03745 and 1.38869.

    J={{-C.sub.84 (A)+{[C.sub.84 (A)].sup.2 -4[C.sub.85 (A)(T)][-C.sub.86 +C.sub.87 (A)√T)-ΔVI]}.sup.1/2 }/2[C.sub.85 (A)(T)]}.sup.2, 13.

where J is the furfural dosage and C₈₄ through C₈₇ are constants havingpreferred values of 0.004074, 5,2758×10⁻⁷, 13.199, and 0.0059403,respectively.

    C=(SOLV) (100)/J                                           14.

where C is the new charge oil flow rate.

Referring now to FIG. 2, signal KV₂₁₀ is provided to an H computer 50 incontrol means 40, while signal KV₁₅₀ is applied to an H computer 50A. Itshould be noted that elements having a number and a letter suffix aresimilar in construction and operation as to those elements having thesame numeric designation without a suffix. All elements in FIG. 2,except elements whose operation is obvious, will be disclosed in detailhereinafter. Computers 50 and 50A provide signals E₁ and E₂corresponding to H₂₁₀ and H₁₅₀, respectively, in equations 1 and 2,respectively, to H signal means 53. K signal means 55 provides a signalE₃ corresponding to the term K₁₅₀ in equation 3 to H signal means 53. Hsignal means 53 provides a signal E₄ corresponding to the term H₁₀₀ inequation 4 to a KV computer 60 which provides a signal E₅ correspondingto the term KV₁₀₀ in accordance with signal E₄ and equation 5 ashereinafter explained.

Signals E₅ and KV₂₁₀ are applied to VI signal means 63 which provides asignal E₆ corresponding to the viscosity index.

An SUS computer 65 receives signal KV₂₁₀ and provides a signal E₇corresponding to the term SUS in accordance with the received signalsand equation 6 as hereinafter explained.

An SUS 210 computer 68 receives signal E₇ and applies signal E₈corresponding to the term SUS₂₁₀ in accordance with the received signaland equation 7 as hereinafter explained.

A W computer 69 receives signals KV₂₁₀, S and API and provides a signalE₉ corresponding to the term W in equation 8 in accordance with thereceived signals and equation 8 as hereinafter explained.

A VI_(DWC).sbsb.O computer 70 receives signal RI, E₉, API, FL and E₆ andprovides a signal E₁₀ corresponding to the term VI_(DWC).sbsb.O inaccordance with the received signals and equation 9 as hereinafterexplained.

A VI_(DWC).sbsb.P computer 72 receives signal E₈ and E₁₀ and provides asignal E₁₁ corresponding to the term VI_(DWC).sbsb.P in accordance withthe received signals and equation 10. Subtracting means 76 performs thefunction of equation 11 by subtracting signal E₁₁ from a direct currentvoltage V₉, corresponding to the term VI_(RP), to provide a signal E₁₂corresponding to the term ΔVI in equation 11.

An A computer 78 receives signals KV₂₁₀, API,S and FL and provides asignal A corresponding to the term A in equation 12, in accordance withthe received signals and equation 12 as hereinafter explained.

A J computer 80 receives signals T, A and E₁₂ and provide a signal E₁₃corresponding to the term J in accordance with the received signals andequation 13 as hereinafter explained to a divider 83.

Signal SOLV is provided to a multiplier 82 where it is multiplied by adirect current voltage V₂ corresponding to a value of 100 to provide asignal corresponding to the term (SOLV) (100) in equation 14. Theproduct signal is applied to divider 83 where it is divided by signalE₁₃ to provide signal C corresponding to the desired new charge oil flowrate.

It would be obvious to one skilled in the art that if the charge oilflow rate was maintained constant and the furfural flow rate varied,equation 14 would be rewritten as

    SO=(J) (CHG)/100                                           15.

where SO is the new solvent flow rate. Control means 40 would bemodified accordingly.

Referring now to FIG. 3, H computer 50 includes summing means 112receiving signal KV₂₁₀ and summing it with a direct current voltage C₁to provide a signal corresponding to the term [KV₂₁₀ +C₁ ] shown inequation 1. The signal from summing means 112 is applied to a naturallogarithm function generator 113 which provides a signal correspondingto the natural log of the sum signal which is then applied to anothernatural log function generator 113A which in turn provides signal E₁.

Referring now to FIG. 4, K signal means 55 includes summing means 114direct current voltages T₁₅₀ and C₃ to provide a signal corresponding tothe term [T₁₅₀ +C₃ ] which is provided to a natural log functiongenerator 113B which in turn provides a signal corresponding to thenatural log of the sum signal from summing means 114. Subtracting means115 subtracts the signal provided by function generator 113B from adirect current voltage C₂ to provide a signal corresponding to thenumerator of equation 3. A divider 116 divides the signal fromsubtracting means 115 with a direct current voltage C₄ to provide signalE₃.

Referring now to FIG. 5, H signal means 53 includes subtracting means117 which subtracts signal E₁ from signal E₂ to provide a signalcorresponding to the term H₁₅₀ -H₂₁₀, in equation 4, to a divider 118.Divider 118 divides the signal from subtracting means 117 by signal E₃.Divider 114 provides a signal which is summed with signal E₁ by summingmeans 119 to provide signal E₄ corresponding to H₁₀₀.

Referrning now to FIG. 6, a direct current voltage V₃ is applied to alogarithmic amplifier 120 in KV computer 60. Direct current voltage V₃corresponds to the mathematical constant e. The output from amplifier120 is applied to a multiplier 122 where it is multiplied with signalE₄. The product signal from multiplier 122 is applied to an antilogcircuit 125 which provides a signal corresponding to the term exp (H₁₀₀)in equation 5. The signal from circuit 125 is multiplied with the outputfrom logarithmic amplifier 120 by a multiplier 127 which provides asignal to antilog circuit 125A. Circuit 125A is provided to subtractingmeans 128 which subtracts a direct current voltage C₁ from the signalfrom circuit 125A to provide signal E₅.

Referring now to FIG. 7, VI signal means 63 is essentially memory meanswhich is addressed by signals E₅, corresponding to KV₁₀₀, and signalKV₂₁₀. In this regard, a comparator 130 and comparator 130A represent aplurality of comparators which receive signal E₅ and compare signal E₅to reference voltages, represented by voltages R₁ and R₂, so as todecode signal E₅. Similarly, comparators 130B and 130C represent aplurality of comparators receiving signal KV₂₁₀ which compare signalKV₂₁₀ with reference voltages RA and RB so as to decode signal KV₂₁₀.The outputs from comparators 130 and 130B are applied to an AND gate 133whose output controls a switch 135. Thus, should comparators 130 and130B provide a high output, AND gate 133 is enabled and causes switch135 to be rendered conductive to pass a direct current voltage V_(A)corresponding to a predetermined value, as signal E₆ which correspondsto VI. Similarly, the outputs of comparators 130 and 130C control an ANDgate 133A which in turn controls a switch 135A to pass or to block adirect current voltage V_(B). Similarly, another AND gate 133B iscontrolled by the outputs from comparators 130A and 130B to control aswitch 135B so as to pass or block a direct current voltage V_(C).Again, an AND gate 133C is controlled by the outputs from comparators130A and 130C to control a switch 135C to pass or to block a directcurrent voltage V_(D). The outputs of switches 135 through 135C are tiedtogether so as to provide a common output.

Referring now to FIG. 8, the SUS computer 65 includes multipliers 136,137 and 138 multiplying signal KV₂₁₀ with direct current voltages C₉, C₇and C₅, respectively, to provide signals corresponding to the terms C₉(KV₂₁₀), C₇ (KV₂₁₀) and C₅ (KV₂₁₀), respectively in equation 6. Amultiplier 139 effectively squares signal KV₂₁₀ to provide a signal tomultipliers 140, 141. Multiplier 140 multiplies the signal frommultiplier 139 with a direct current voltage C₁₀ to provide a signalcorresponding to the term C₁₀ (KV₂₁₀)² in equation 6. Multiplier 141multiplies the signal from multiplier 139 with signal KV₂₁₀ to provide asignal corresponding to (KV₂₁₀)³. A multiplier 142 multiplies the signalfrom multiplier 141 with a direct current voltage C₁₁ to provide asignal corresponding to the term C₁₁ (KV₂₁₀)³ in equation 6. Summingmeans 143 sums the signals from multipliers 136, 140 and 142 with adirect current voltage C₈ to provide a signal to a multiplier 144 whereit is multiplied with a direct current voltage C₁₂. The signal frommultiplier 137 is summed with a direct current voltage C₆ by summingmeans 145 to provide a signal corresponding to the term [C₆ +C₇ (KV₂₁₀]. A divider 146 divides the signal provided by summing means 145 withthe signal provided by multiplier 144 to provide a signal which issummed with the signal from multiplier 138 by summing means 147 toprovide signal E₇.

Referring now to FIG. 9, SUS₂₁₀ computer 68 includes subtracting means148 which subtracts a direct current voltage C₁₆ from another directcurrent voltage C₁₆ from another direct current voltage C₁₅ to provide asignal corresponding to the term (C₁₅ -C₁₆) in equation 7. The signalfrom subtracting means 148 is multiplied with a direct current voltageC₁₄ by a multiplier 149 to provide a product signal which is summed withanother direct current voltage C₁₃ by summing means 150. Summing means150 provides a signal corresponding to the term [C₁₃ +C₁₄ (C₁₅ -C₁₆ ] inequation 7. The signal from summing means 150 is multiplied with signalE₇ by a multiplier 152 to provide signal E₈.

Referring now to FIG. 10, there is shown W computer 69 havingmultipliers 155, 156 and 157 receiving signal API. Multiplier 155multiplies signal API with signal S to provide a product signal toanother multiplier 160 where it is multiplied with a direct currentvoltage C₄₉ to provide a signal corresponding to the term C₄₉ (S) (API)in equation 8. Multiplier 156 effectively squares signal API andprovides a signal to another multiplier 163 where it is multiplied witha direct current voltage C₄₇ to provide a signal corresponding to theterm (C₄₇) (API)². Multiplier 157 multiplies signal API with a directcurrent voltage C₄₄ to provide a signal corresponding to the term C₄₄(API). A divider 166 divides signal API with signal KV₂₁₀ to provideanother signal to a multiplier 168 where it is multiplied with a directcurrent voltage C₄₈ which in turn provides a signal corresponding to theterm [C₄₈ (API)/(KV₂₁₀)] in equation 8. A divider 170 divides a directcurrent voltage C₄₅ with signal KV₂₁₀ to provide a signal correspondingto the term C₄₅ /(KV₂₁₀). A multiplier 173 multiplies signal S with adirect current voltage C₄₆. Summing means 175 sums a direct currentvoltage C₄₃ with the signals provided by multipliers 160, 163 anddivider 170. Other summing means 176 sums the signals provided bymultipliers 157, 168 and 173. Subtracting means 179 subtracts the signalprovided by summing means 176 from the signal provided by summing means175 to provide signal E₉.

Referring now to FIG. 11, VI_(DWC).sbsb.O computer 70 includes amultiplier 180 which effectively squares signal KV₂₁₀ and provides it toa multiplier 181 where it is multiplied with direct current voltage C₆₈.Multiplier 181 provides a signal corresponding to the term C₆₈ (KV₂₁₀)²in equation 9. A multiplier 182 multiplies signals KV₂₁₀, E₉ to providea signal to another multiplier 183 where it is multiplied with directcurrent voltage C₇₃. Multiplier 183 provides a signal corresponding tothe term C₇₃ (W) (KV₂₁₀) in equation 9. A multiplier 184 multipliessignal E₆ with a direct current voltage C₆₉ to provide a signalcorresponding to the term C₆₉ (VI) in equation 9. Another multiplier 185multiplies signals E₆, FL to provide a signal to a multiplier 186 whereit is multiplied with a direct current voltage C₇₂. Multiplier 186provides a signal corresponding to the term C₇₂ (FL) (VI) in equation 9.A multiplier 188 multiplies signals E₆, API to provide a signal toanother multiplier 189 where it is multiplied with direct currentvoltage C₇₀. Product signals provided by multipliers 183, 189 are summedwith another direct current voltage C₆₇ by summing means 192 to providea signal corresponding to the term -C₆₇ -C₇₀ (API) (VI)-C₇₃ (W) (KV₂₁₀).A multiplier 193 effectively squares signal API and provides it to amultiplier 194 where it is multiplied with a direct current voltage C₇₁.Multiplier 194 provides a signal corresponding to the term C₇₁ (API)² inequation 9. Summing means 197 sums the signal from multipliers 181, 184,186 and 196. Subtracting means 199 subtracts the signal provided bysumming means 192 from the signal provided by summing means 197 toprovide signal E₁₀.

VI_(DWC).sbsb.P computer 72 shown in FIG. 12, includes a naturallogarithm function generator 200 receiving signal E₈ and providing asignal corresponding to the term lnSUS₂₁₀ to multipliers 201 and 202.Multiplier 201 multiplies the signal from function generator 200 with adirect current voltage C₂₂ to provide a signal corresponding to the termC₂₂ ln SUS₂₁₀ in equation 10. Multiplier 202 effectively squares thesignal from function generator 200 to provide a signal that ismultiplied with the direct current voltage C₂₃ by a multiplier 205.Multiplier 205 provides a signal corresponding to the term C₂₃ (lnSUS₂₁₀)² in equation 10. Subtracting means 206 subtracts the signalsprovided by multiplier 201 from the signal provided by multiplier 205.Summing means 207 sums the signal from subtracting means 206 with adirect current voltage C₂₁. A multiplier 208 multiplies the sum signalsfrom summing means 207 with a direct current voltage POUR to provide asignal which is summed with signal E₁₀ by summing means 210 whichprovides signal E₁₁ .

FIG. 13 shows A computer 78 having a multiplier 215 effectively squaringsignal KV₂₁₀ to provide a signal which is multiplied with a directcurrent voltage C₇₅ by a multiplier 216 which provides a signalcorresponding to the term C₇₅ (KV₂₁₀)² in equation 12. Multiplier 218multiplies signals KV₂₁₀, S to provide a signal that is multiplied witha direct current voltage C₇₉ by a multiplier 220. Multiplier 220provides a signal corresponding to the term C₇₉ (KV₂₁₀) (S) in equation12. A multiplier 223 multiplies signals API, FL to provide a signal toanother multiplier 224 where it multiplies a direct current voltage C₇₈.Multiplier 224 provides a signal corresponding to the term C₇₈ (FL)(API) in equatiion 12. Summing means 226 essentially sums all of thenegative terms in equation 12 by summing the signals from multipliers216, 220 and 224. A multiplier 229 multiplies signal S with a directcurrent voltage V₇₆ to provide a signal corresponding to the term C₇₆(S) in equation 12. Another multiplier 230 effectively squares signal FLand provides it to yet another multiplier 231 where it is multipliedwith a direct current voltage C₇₇. Multiplier 231 provides a signalcorresponding to the term C₇₇ (FL)². Summing means 235 essentially sumsthe positive terms of equation 12 by summing a direct current voltageC₇₄ with the signals provided by multipliers 229 and 231. Subtractingmeans 237 subtracts the signals provided by summing means 236 from thesignal provided by summing means 235 to provide signal A.

Referring to FIG. 14, J computer 80 includes a square root circuit 240receiving signal T and providing a signal to a multiplier 241 where itis multiplied with signal A. Multiplier 241 provides a signal to anothermultiplier 242 where it is multiplied with a direct current voltage C₈₇.Multiplier 242 provides a signal corresponding to the term C₈₇ (A) (√T)in equation 13. Subtracting means 243 subtracts a direct current voltageC₈₆ from the signal provided by multiplier 242 to provide a differencesignal. Subtracting means 244 subtracts signal E₁₂ from the differencesignal provided by subtracting means 243.

A multiplier 245 multiplies signals T and A to provide a signal toanother multiplier 246 where it is multiplied with direct currentvoltage C₈₅. Multiplier 246 provides a signal, corresponding to the term[C₈₅ (A)(T)] in equation 13, to multipliers 250 and 251. Multiplier 250multiplies the signal from multiplier 246 with direct current voltage V₄to provide a signal to multiplier 255 where it is multiplied with thesignal from subtracting means 244. Multiplier 251 multiplies the signalfrom multiplier 246 with voltage V₂₃, corresponding to a value of 2.

A multiplier 256 multiplies signal A with a direct current voltage C₈₄to provide a signal to a multiplier 257 which effectively squares thesignal. Multiplier 257 provides a signal corresponding to the term [C₈₄(A)]² in equation 13. Subtracting means 260 subtracts the signalprovided by multiplier 255 from the signal provided by multiplier 257 toprovide a signal to square root circuit 262. Subtracting means 264subtracts the signal provided by multiplier 256 from the signal providedby square root circuit 262 to develop a signal. A divider 265 dividesthe signal from subtracting means 264 with the signal from multiplier251 to provide a signal that is squared by a multiplier 267 whichprovides signal E₁₃.

The present invention as hereinbefore described controls a solventrefining unit receiving heavy sour charge oil to achieve a desiredcharge oil flow rate for a constant furfural flow rate. It is alsowithin the scope of the present invention, as hereinbefore described, tocontrol the furfural flow rate while the heavy sour charge oil flow ismaintained at a constant rate.

What is claimed is:
 1. A control system for a furfural refining unitreceiving heavy sour charge oil and furfural solvent, one of which ismaintained at a fixed flow rate while the flow rate of the other iscontrolled by the control system, treats the received heavy sour chargeoil with the received furfural to yield extract mix and raffinate,comprising gravity analyzer means for sampling the heavy sour charge oiland providing a signal API corresponding to the API gravity of the heavysour charge oil, flash point analyzer means for sampling the heavy sourcharge oil and providing a signal FL corresponding to the flash pointtemperature of the heavy sour charge oil, viscosity analyzer means forsampling the heavy sour charge oil and providing signals KV₁₅₀ and KV₂₁₀corresponding to the kinematic viscosities, corrected to 150° F. and210° F., respectively, sulfur analyzer for sampling the heavy sourcharge oil and providing signal S corresponding to the sulfur content ofthe heavy sour charge oil, flow rate sensing means for sensing the flowrates of the heavy sour charge oil and of the furfural and providingsignals CHG and SOLV, corresponding to the heavy sour charge oil flowrate and the furfural flow rate, temperature sensing means sensing thetemperature of the extract mix and providing a corresponding signal T,and control means connected to all of the analyzer means, and to thesensing means for controlling the other flow rate of the charge oil andthe furfural flow rates in accordance with signals API, FL, KV₁₅₀,KV₂₁₀, S, CHG and SOLV; said control means includes VI signal meansconnected to the viscosity analyzer means for providing a signal VIcorresponding to the viscosity index of the heavy sour charge oil inaccordance with the kinematic viscosity signals KV₁₅₀ and KV₂₁₀ ; SUS₂₁₀signal means connected to the viscosity analyzer means for providing asignal SUS₂₁₀ corresponding to the heavy sour change oil viscosity inSaybolt Universal Seconds corrected to 210° F.; W signal means connectedto the viscosity analyzer means, to the gravity analyzer means and tothe sulfur analyzer means for providing a signal W corresponding to thewax content of the heavy sour charge oil in accordance with signalsKV₂₁₀, API and S, A signal means connected to the gravity analyzermeans, to the viscosity analyzer means, to the sulfur analyzer means, tothe flash point temperature analyzer means and to the VI signal meansfor providing a signal A corresponding to an interim factor A inaccordance with signals KV₂₁₀, S, API, VI and FL; ΔVI signal meansconnected to the viscosity analyzer means, to the gravity analyzermeans, to the flash point temperature analyzer means, to the VI signalmeans, the W signal means and the SUS₂₁₀ signal means and receivingvoltage VI_(RP) for providing a signal ΔVI corresponding to the changein viscosity index in accordance with signals KV₂₁₀, API, VI, FL, W andSUS₂₁₀ and voltage VI_(RP), J signal means receiving direct currentvoltages corresponding to values of constants C₈₄ through C₈₇ and beingconnected to the ΔVI signal means, to the A signal means, to thetemperature sensing means for providing a J signal corresponding to afurfural dosage for heavy sour charge oil in accordance with the ΔVIsignal, signals A and T, the received voltages and the followingequation:

    J={{-C.sub.84 (A)+{[C.sub.84 (A)].sup.2 -4[C.sub.85 (A)(T)][-C.sub.86 +C.sub.87 (A)(√t)-ΔVI}.sup.1/2 }/2[C.sub.85 (A)(T)]}.sup.2


2. a system as described in claim 1 in which the SUS₂₁₀ signal meansinclude SUS signal means connected to the viscosity analyzer means, andthe receiving direct current voltages C₅ through C₁₂ for providing asignal SUS corresponding to an interim factor SUS in accordance withsignal KV₂₁₀, voltages C₅ through C₁₂ and the following equation:

    SUS=C.sub.5 (KV.sub.210)+[C.sub.6 +C.sub.7 (KV.sub.210)]/[C.sub.8 +C.sub.9 (KV.sub.210)+C.sub.10)KV.sub.210).sup.2 +C.sub.11)KV.sub.210).sup.3 ](C.sub.12),

where C₅ through C₁₂ are constants; and SUS₂₁₀ network means connectedto the SUS signal means and to the ΔVI signal means and receiving directcurrent voltages C₁₃ through C₁₆ for providing signal SUS₂₁₀ to the ΔVIsignal means in accordance with signal SUS, voltages C₁₃ through C₁₆ andthe following equation:

    SUS.sub.210 =[C.sub.13 +C.sub.14)C.sub.15 -C.sub.16)]SUS,

where C₁₃ through C₁₆ are constants.
 3. A system as described in claim 2in which the W signal means further receives direct current voltages C₄₃through C₄₉ and provides signal W in accordance with signals API, KV₂₁₀and S, voltages C₄₃ through C₄₉, and the following equation:

    W=C.sub.43 -C.sub.44 API+C.sub.45 /KV.sub.210 -C.sub.46 S+C.sub.47)API).sup.2 -C.sub.48 API/KV.sub.210 +C.sub.49 (S)(API),

where C₄₃ through C₄₉ are constants.
 4. A system as described in claim 3in which the VI signal means includes K signal means receiving directcurrent voltages C₂, C₃, C₄ and T₁₅₀ for providing a signal K₁₅₀corresponding to the kinematic viscosity of the charge oil corrected to150° F. in accordance with voltages C₂, C₃, C₄ and T₁₅₀, and thefollowing equation:

    K.sub.150 +[C.sub.2 -ln(T.sub.150 +C.sub.3)]C.sub.4

where C₂ through C₄ are constants, and T₁₅₀ corresponds to a temperatureof 150° F.; H₁₅₀ signal means connected to the viscosity analyzer meansand receiving a direct current voltage C₁ for providing a signal H₁₅₀corresponding to a viscosity H value for 150° F. in accordance withsignal KV₁₅₀ and voltage C₁ in the following equation:

    H.sub.150 =lnln(KV.sub.150 +C.sub.1)

where C₁ is a constant; H₂₁₀ signal means connected to the viscosityanalyzer means and receiving voltage C₁ for providing signal H₂₁₀corresponding to a viscosity H value for 210° F. in accordance withsignal KV₂₁₀, voltage C₁ and the following equation:

    H.sub.210 =lnln(KV.sub.210 +C.sub.1)

H₁₀₀ signal means connected to the K signal means, to the H₁₅₀ signalmeans and the H₂₁₀ signal means for providing a signal H₁₀₀corresponding to a viscosity H value for 100° F., in accordance withsignals H₁₅₀, H₂₁₀ and K₁₅₀ and the following equation:

    H.sub.100 =H.sub.210 +(H.sub.150 -H.sub.210)/K.sub.150

Kv₁₀₀ signal means connected to the H₁₀₀ signal means and receivingvoltage C₁ for providing a signal KV₁₀₀ corresponding to a kinematicviscosity for the charge oil corrected to 100° F. in accordance withsignal H₁₀₀, voltage C₁, and the following equation:

    KV.sub.100 =exp[exp(H.sub.100)]-C

and VI memory means connected to the KV₁₀₀ signal means and to theviscosity analyzer means having a plurality of signals stored therein,corresponding to different viscosity index and controlled by signalsKV₁₀₀ and KV₂₁₀ to select a stored signal and providing the selectedstored signal as signal VI.
 5. A system as described in claim 4 in whichthe A signal means also receives direct current voltages correspondingto constants C₇₄ through C₇₉ and provides signal A in accordance withsignals KV₂₁₀, S, FL, and API, the received voltages and the followingequation:

    A=C.sub.74 -C.sub.75 (KV.sub.210).sup.2 +C.sub.76 (S)+C.sub.77 (FL).sup.2 -C.sub.78 (FL)(API)-C.sub.79 (KV.sub.210)(S)


6. A system as described in claim 5 in which the ΔVI signal meansincludes a VI_(DWCO) signal means connected to viscosity analyzer means,to the gravity analyzer means, to the flash point temperature analyzermeans, to the VI signal means, to the W signal means and receivingdirect current voltages corresponding to values of constants C₆₇ throughC₇₃ for providing a signal VI_(DWCO) in accordance with signals KV₂₁₀,VI, API, FL and W, voltages C₆₇ through C₇₃, and the following equation:

    VI.sub.DWC.sbsb.O =C.sub.67 +C.sub.68 (KV.sub.210).sup.2 +C.sub.69 (VI)-C.sub.70 (API)(VI)+C.sub.71 (API).sup.2 +C.sub.72 (FL)(VI)-C.sub.73 (W)(KV.sub.210)

a VI_(DWCP) signal means connected to the VI_(DWCO) signal means and tothe SUS₂₁₀ signal means, and receiving direct current voltagescorresponding to values of constants C₂₁ through C₂₃ and to the pourpoint of dewaxed refined oil for providing a signal VI_(DWCP) inaccordance with signal VI_(DWCO) and SUS₂₁₀, the received voltages andthe following equation:

    VI.sub.DWC.sbsb.P =VI.sub.DWC.sbsb.O +(POUR)[C.sub.21 -C.sub.22 lnSUS.sub.210 +C.sub.23 (lnSUS.sub.210).sup.2 ]

where POUR is the pour point of the dewaxed refined oil, and subtractingmeans connected to the VI_(DWCP) signal means and to the J signal meansand receiving direct voltage VI_(RP) for subtracting signal VI_(DWCP)from voltage VI_(RP) to provide the ΔVI signal to the J signal means. 7.A system as described in claim 6 in which the flow rate of the heavysour charge oil is controlled and the flow of the furfural is maintainedat a constant rate and the control signal means receives signal SOLVfrom the flow rate sensing means, the J signal from the J signal meansand a direct current voltage corresponding to a value of 100 andprovides a signal C to the apparatus means corresponding to a new heavysour charge oil flow rate in accordance with the J signal, signal SOLVand the received voltage and the following equation:

    C=(SOLV)(100)/J

so as to cause the apparatus means to change the charge oil flow to thenew flow rate.
 8. A system as described in claim 6 in which thecontrolled flow rate is the furfural flow rate and the flow of the heavysour charge oil is maintained constant, and the control signal means isconnected to the sensing means, to the J signal means and receives adirect current voltage corresponding to the value of 100 for providing asignal SO corresponding to a new furfural flow rate in accordance withsignals CHG and the J signal and the received voltage, and the followingequation:

    SO=(CHG)(J)/100

so as to cause the furfural flow to change to the new flow rate.